Forthcoming releases of the 3GPP LTE (3rd Generation Partnership Project Long Term Evolution) and HSPA (High Speed Packet Access) standard facilitate dual-carrier operation. In dual carrier operation, the user equipment (UE) can transmit and receive on multiple system carriers simultaneously. A dual carrier system 100 is illustrated in FIG. 1. A dual carrier capable UE 112 can transmit to, and receive from, serving cell 110 on multiple system carriers (f1 and f2) simultaneously. A dual carrier system can increase the maximal throughput. Throughput is roughly proportional to N where N is the number of carriers. Therefore, the throughput in a dual carrier system can increase by a factor of two (from 100 Mb/s to 200 Mb/s for example). A dual-carrier (or dual-cell) mobile terminal (or UE) for use in the dual carrier system needs the ability to process two downlinks (and/or two uplinks) at the same time. Typically, this means that baseband processing capability of a dual-carrier mobile terminal (such as channel estimation/decoding, etc.) is double that of a single-carrier mobile terminal.
The co-ordination of transmission from antennas positioned in different sites have also evolved in these standards such as advanced Inter-Cell Interference Co-ordination (ICIC), Co-ordinated MultiPoint (CoMP) transmission and the introduction of Remote Radio Units (RRU). These techniques enable fast co-ordinated transmissions from several antenna positions including beam forming and nulling. With nulling, interference can be strongly reduced to a specific UE. In coherent CoMP transmissions, the nulling gain is included in the algorithm of selecting co-scheduled mobiles and antenna pre-coding weights.
In order to increase capacity, MU-MIMO (Multi User Multiple Input Multiple Output) is used. In MU-MIMO, the radio resources are reused by transmitting on the same time and frequency to multiple UEs.
Dual-carrier (dual-cell) LTE/HSPA will probably be applied only in hot spot regions and also is only needed for very high throughput scenarios such as when single carrier transmission is insufficient. Therefore, in many use cases, where a single carrier is used, the baseband processing is not fully utilized in the mobile terminal. According to a common scenario in cellular systems, as illustrated in FIG. 2, a terminal 212 is at the cell border between two cells. One of these cells is the serving cell (SC) 210 and the other cell is a neighboring cell (NC) (or multiple neighboring cells) 220. A signal S that is being communicated between serving cell 210 and UE 212 is being subjected to interference I from neighboring cell 220. In such a scenario, the signal-interference-ratio (SI or SIR or carrier-to-interference ratio, CA) is approximately 0 dB (SI≈0). As a result, full downlink (DL) (and uplink, UL) throughput cannot be achieved. However, in these scenarios, the extra processing power can be used for detecting and cancelling the interfering signals, I.
A terminal connected to a cell receives control information on the physical downlink control channel (PDCCH). This information can be utilized by the terminal to determine whether it (i.e. the terminal) is scheduled in the downlink in the current subframe. The terminal attempts to blindly decode multiple PDCCHs in each subframe. If the decoding is successful, it (i.e. decoded information) contains the parameters necessary to receive the data transmission. PDCCH also provides information about resource blocks and modulation and coding used for data transmission (i.e. for data transmitted on the physical downlink shared channel, PDSCH).
However, a significant problem that is encountered in the cancellation scenario is obtaining information about the scheduled users. This information (about scheduled users) is needed to receive the signal from the neighboring cell which can be used in the cancellation process. Blind decoding of the PDCCHs transmitted in the neighboring cell is typically not feasible as the terminal (that is decoding the PDCCHs) is unaware of which terminals are connected to the neighboring cells. This makes the cancelling process significantly more complex.
There exists a need therefore for a method and apparatus for improving the blind PDCCH decoding in the mobile terminal in order to enable the terminal to do advanced interference cancelling of signals transmitted from neighboring cells to corresponding neighboring mobile terminals.
Furthermore, when transmission schemes such as beam forming, nulling, MU-MIMO or CoMP is used, it is desirable to take the UE interference cancellation capability into account when selecting pre-coding as well as to select the group of UEs to co-schedule on the same radio resources.